As used herein, the words "multichip module", singular or plural, are intended to refer to an electronic assembly which has therein a plurality of interconnected components (e.g., transistors, diodes, integrated circuits, resistors, capacitors, inductors, etc., or combinations thereof). As used herein, the word "chip", singular or plural, is intended to refer generally to any type of component within the multichip module. The particular choices of components and their arrangement and interconnection with the multichip module are outside the scope of the present invention.
Multichip modules are much used in modern day electronic equipment, especially equipment where high performance, reliability and ruggedness are important. Oftentimes, in order to fully test a multichip module it is necessary to provide a hermetic lid or cap in order to protect the chips and wiring therein from the ambient atmosphere during testing. This is especially true where the tests include temperature and/or humidity extremes. In the event that the tests show that one or more chips within the module must be replaced or that some portion of the wiring must be repaired, then one must be able to decap the module without damaging any of the internal parts or interfering with the ability to reseal the module after repairs are completed. AS used herein, the words "lid", "cap" and "cover", singular or plural, are intended to have the same meaning and include any removable means (other than potting compounds or conformal coatings) for closing a multichip module to protect it from the ambient atmosphere.
One prior art means for obtaining a resealable multichip module is to provide a lid held in place by screws or clamps and sealed by gaskets. While such arrangement may be readily sealed, opened for repair and then resealed, it is generally expensive and bulky and does not usually provide a high degree of long term hermeticity after closure.
Another arrangement which has been used in the prior art is to seal the lid to the module base with metal or glass solders or brazing materials. Unless specifically indicated, the word "solder", singular or plural, as used herein, is intended to refer to glasses, metals and combinations thereof that soften or melt when heated and which are usable for joining various materials and encompass those materials conventionally used for soldering or brazing. While solder seals can generally provide a high degree of hermeticity, modules sealed in this manner are difficult to open and reseal. This is because, glass solders tend to devitrify and/or metal solders tend to alloy with the lid and module materials during the initial sealing operation, so that the thermal and mechanical properties of the solder are different after the initial seal is completed. Thus, when one attempts to decap a solder sealed module, the solder may require a much higher temperature to soften or melt enough to permit lid removal and resealing, with a consequent adverse impact on the chips and wiring within the module. Further, it may be difficult or impossible to achieve hermetic closure during reseal after repairs are completed.
Modules that are welded closed must have the weld ground off or etched off in order to be opened for repair. Such operations generally introduce undesirable particulate material and other contaminates into the module during decapping. Also, it may be difficult or impossible to reweld the package after repairs are complete. Hence, opening and resealing of welded modules is generally undesirable.
Thus, there continues to be a need for improved means and method for multichip modules that may be temporarily sealed to a substantially hermetic condition (e.g., to permit adequate testing) and, if necessary, decapped for repairs, and then resealed or further sealed in a manner that promotes long term hermeticity.
Accordingly, it is an advantage of the present method to provide an improved means and method for temporarily sealing multichip modules so that, for example, tests may be performed and then, if necessary, decapped for repairs and then resealed or further sealed using materials or techniques generally known to provide good long term hermeticity. It is a further advantage to provide such without use of gaskets with screws or clamps. It is a still further advantage to provide such in a manner that readily adapts to different base and lid configurations. It is a yet further advantage to provide such in a manner that avoids the decapping and resealing problems associated with prior art glass or metal solders.